The invention concerns a method for the automatic lambda control of an internal combustion engine.
To maintain the legal pollutant limits, an internal combustion engine is automatically controlled to a set lambda value. In this closed-loop control system, a pump current of the lambda sensor is determined as a measured value. This is then converted to an actual lambda value and compared with the set lambda value to obtain a lambda control deviation. A lambda controller then uses the lambda control deviation to compute the control signal, for example, a set injection quantity, with which an injector is then activated. Based on the raw environment in the exhaust gas tract of the internal combustion engine, the lambda sensor ages over its operating time, so that the signal of the measured value changes. However, to achieve high precision, the lambda sensor must be calibrated at regular intervals, for example, after about 24 hours of operation.
DE 10 2005 056 152 A1 discloses a method for calibrating a lambda sensor. When a predetermined operating state of the internal combustion engine is detected, a correction value for adjusting the measured value is determined. The adjusted measured value then corresponds to the actual lambda value. The predetermined operating state is defined as the state in which the injection is deactivated and the speed of the internal combustion engine is above a threshold engine speed, in other words, during a shifting operation of the internal combustion operation or a coasting phase of the vehicle. However, the method is thus limited to a vehicle application, for example, an automobile or truck. In so-called off-road applications, for example, in an internal combustion engine that drives a bagger or a pump for delivering oil, there is no coasting phase. Therefore, the method described above cannot be used for these applications.